Field of the Invention
The invention relates to a laminate for application on a support material, in particular on a support plate, with a resin-impregnated decorative layer and with at least one resin-impregnated core layer, wherein the decorative layer and the at least one core layer are suitable to be pressed together under high pressure and heat by means of a multi piston press. The invention also relates to a method for producing a laminate.
Description of Related Art
Laminates known from the prior art of the DE 199 42 972 A1, DE 103 16 884 A1, U.S. Pat. Nos. 3,738,900 A, 4,062,992, and the U.S. Pat. No. 4,140,837 A are an extremely versatile material that can be processed in combination with wooden materials or other carrier materials to form so-called composite elements. The applications are diverse and require the use of various laminate qualities that can be adapted to the subsequent areas of use. Conventional applications and areas of use include for example the kitchen sector, door hardware, office furniture equipment, exhibition construction, shop-fitting, decorative interior fittings, flooring, ship building and vehicle construction. Laminates are thus understood to include decorative materials that can satisfy different requirements. There are for example standard quality laminates, re-mouldable decorative laminates that can also be shaped at higher temperatures, or decorative laminates with improved fire behaviour.
The laminates include decorative laminates based on curable resins. They are composed of several layers and consist for example of at least one melamine resin-impregnated decorative paper as decorative layer and one or more natron kraft papers impregnated with phenol resin as core layers, which can be pressed together under high pressure and heat. The laminate structure, resin and paper qualities, surface structures, the use of special overlays (protective layers) as well as the pressing parameters in the production are decisive in regard to the laminate quality and thus for the subsequent application and area of use.
The decorative side of the laminate, the decorative layer, can consist of decorative paper, which is printed as wood decoration or fantasy decoration, or may consist of uni-decorations or white decorations, which are formed for example as plastic layers. The surface weights of the decorative papers are generally between 50 and 160 g/m2.
An essential constituent of laminates may be core papers, for example natron kraft papers, which are also called core layers or core plies. The surface weight of the core papers and natron kraft papers is in the range from 70 to 300 g/m2, wherein high grammages are mainly used for compact panels.
An overlay is a bleached, transparent paper with a high resin absorption capability and is used to protect the decoration, in particular the printed image of printed decorative papers and to improve the abrasion resistance.
An underlay or barrier paper is a paper layer between the decorative and core or natron kraft paper, which is used to prevent chemical reaction between the resins or to achieve optical effects.
Melamine-formaldehyde resins form transparent and hard coatings and are therefore best suited as surface layer of decorative laminates. To impregnate the core layers relatively elastic phenol-formaldehyde resins are used, not only for cost reasons.
Decorative laminates can therefore consist of cellulose fibre webs or papers, which are impregnated with thermosetting resins. Other natural or synthetic materials can also be used as carrier material for the resins. Thus, laminates of fibreglass matting impregnated with resin are known. The layers, preferably the paper layers, are joined to one another to form the laminate by the production methods described hereinafter. The application of heat and pressure thereby causes the resins to flow and subsequently harden. Owing to the crosslinking of the resins, preferably enhanced by the cellulose fibres of the papers, a very dense material with a closed surface is formed. In this connection individual paper layers, and also an outer paper layer, may be un-impregnated before the pressing, since during pressing the resin also penetrates previously un-impregnated layers.
At the start of the method the layers of the laminate are placed above one another and are then brought between two pressing means in the form of press plates or press belts. These pressing means are heated to a predetermined temperature, so that during the pressing procedure not only a sufficient pressure but also the necessary temperature is applied to the layers. The high-pressure method is thus defined by the simultaneous application of heat (temperature ≥120° C.) and a high pressure (≥25 bar), so that the thermosetting resins flow and then harden, in order to produce a homogeneous, non-porous material of increased density (≥1.35 g/cm3) and of the required surface finish.
The aforementioned pressing means normally have a very smooth surface in order to achieve a correspondingly smooth and therefore shiny surface of the laminate. It is also known to provide the pressing means applied to the side of the decorative layer with a macroscopic structure, in order to produce a visible surface structure, possibly synchronised with the decoration. This leads together with the decoration to an improved natural-looking surface appearance. In the case of endless production by means of a double-belt press the production of synchronised structures is however not possible or only possible under very stringent conditions, on account of the fluctuating paper growth and on account of the slippage between the steel belt and workpiece. With multi daylight presses on the other hand depending on the structure press plates corresponding to the number of platens of the press would have to be available, which is extremely uneconomical.
Known production methods include CPL methods, where CPL is the abbreviation for continuous pressed laminates, and HPL methods, where HPL is the abbreviation for high pressure laminates.
CPL are produced in continuously operating double-belt presses with a pressure between 25 and 50 bar and temperatures between 150° C. and 170° C. The feed rate varies between 8 and 30 m/min depending on the laminate thickness and the pressing zone length.
HPL are up to now produced in discontinuously operating multi daylight presses, in which a plurality of units consisting of two press plates and layers arranged in between are stacked above one another, which are pressed in a single pressing step at a pressure between 70 and 80 bar and temperatures of more than 120° C. The multi-daylight presses can have up to 45 platens and each platen can be filled with up to 24 laminate layers (thickness ca. 0.50 to 1.90 mm). Depending on the press loading and the maximum temperature the complete pressing cycle including an optional reverse cooling lasts about 100 minutes.
The length and width formatting of HPL takes place in separate work steps before the pressing, in which materials having a width of up to about 1,300 mm can be produced. CPL on the other hand can be cut to width and/or formatted to length or wound onto rollers directly online after the press. The maximum width of CPL is in this case in the region of 1,300 mm.
In addition short-cycle presses are known, in which support materials such as wood material plates can be coated with laminates. Laminates of the present type cannot up to now be pressed on the known short-cycle presses, since the thin laminates cannot compensate for pressure differences over the surface. Because significant differences in pressure occur in conventional short-cycle presses, not least on account of the imprecise control of the press cylinders. With carrier materials of sufficient thickness these pressure differences can however be well compensated by the carrier material, for example a chipboard panel or a medium-density fibre panel.
Furthermore a multi-piston press is known, for example the KT 700 press from the company Siempelkamp. Compared to hitherto installed presses the multi-piston press uses several small hydraulic cylinders, which for their part can be individually controlled. Accordingly very slight tolerances in the parallelism of the press plates can be achieved, so that an extremely regular distribution of the pressing force is reached.
This press is however up to now also only used to coat wood material support plates or to produce compact plates. In particular minimum interspacings of more than 2 mm are preset by mechanical spacers at the factory, which make it impossible to press laminates.
After the production of the laminate, said laminate is bonded, generally in a separate process step and with a time delay, to a support material or a support plate. In order to be able to bond laminates better to a support plate, the rear sides of the latter are ground. By means of the grinding a surface structure is obtained that is easily wettable. The disadvantage of grinding the rear side however is that the laminate thereby becomes unsymmetrical and also tends to bulge. Therefore extremely detailed storage and handling measures and special precautions have to be taken. In addition the processing is therefore also made significantly more complicated.
Furthermore the grinding leads to an at least partial, preferably almost complete abrasion of the topmost resin layer, so that the paper layer arranged underneath is at least partially exposed. The surface tension is therefore reduced and the wettability of the surface alters. Moisture can therefore penetrate into the laminate during storage, before the adhesive can be applied shortly before the processing. In addition the adhesive can in some cases penetrate too deeply into the laminate structure, so that more adhesive than necessary has to be used for the bonding to the support plate.